You can extend many houses in England without a planning application, as long as the extension stays inside a fixed set of limits. These are called permitted development rights. A single-storey rear extension can usually go out 3 metres (4 metres on a detached house), and the larger prior approval route can take that to 6 metres or 8 metres. Side extensions and two-storey extensions are allowed too, but with tighter limits. This guide sets out each limit, the checks that catch people out, and when it is smarter to apply for full permission anyway.
It covers England. Wales, Scotland and Northern Ireland each have their own rules, so do not apply these figures there.
TL;DR
- Permitted development lets you extend without a planning application if you meet every limit and condition, which are set out in the Town and Country Planning (General Permitted Development) (England) Order 2015.
- A single-storey rear extension can go 4 metres beyond the original rear wall on a detached house, or 3 metres on any other house. With prior approval that rises to 8 metres and 6 metres respectively.
- Side extensions must be single-storey, no higher than 4 metres and no wider than half the original house.
- Flats, maisonettes, conservation areas, Article 4 areas and some converted homes lose or reduce these rights, so check before you design anything.
- A Lawful Development Certificate from your council is the cheapest way to prove your extension is lawful.
Table of Contents
- What permitted development actually means
- Does your house qualify?
- The rules that apply to every extension
- Single-storey rear extensions
- Side extensions
- Two-storey extensions
- Conservatory or extension?
- Prove it: the Lawful Development Certificate
- When to apply for planning permission instead
- Our perspective
- Planning an extension in the West Midlands?
- FAQ
- Sources
What permitted development actually means
Planning permission is the council deciding whether your project is acceptable. Permitted development (PD) is Parliament having already decided that certain common projects are acceptable, provided you stay inside the rules. If you do, you do not need to apply.
That does not mean "no approval of any kind". Building regulations still apply to almost any extension, covering structure, insulation, fire safety, drainage and electrics. The Party Wall etc. Act may apply if you build on or near a neighbour's boundary. PD only removes the planning step, and only when your house and your design qualify.
The rules come from Class A, which covers enlargements, improvements and alterations to a house. The official technical guidance for householders is the document councils work from, and it is worth reading alongside this article.
Does your house qualify?
Start here, because it is where most plans fall over. PD rights for extensions do not apply to:
- Flats and maisonettes.
- Houses created through certain change-of-use rights, such as those under Classes M, N, P, PA and Q, according to the same government guidance.
- Houses where an Article 4 Direction has removed the rights.
Two other situations matter in the West Midlands, where there are plenty of conservation areas and older suburbs:
- Designated land. National parks, conservation areas and similar land carry tighter limits. Two-storey extensions, for example, are not permitted there.
- Listed buildings. Listed building consent is a separate regime, and PD does not give you a free hand. Even small changes to finishes can cause trouble, which is why guides such as painting rules for listed buildings are worth reading before you touch a protected property.
An Article 4 Direction is a council order that removes specific PD rights in a defined area. Birmingham, Solihull and neighbouring councils use them, in some cases for particular streets or estates. Your council's planning pages or planning department will tell you whether your address is covered. Do this before you pay for drawings.
The rules that apply to every extension
These conditions sit behind each type of extension, so check them first.
Original house, not current house
All the measurements run from the "original house", meaning the building as first built or as it stood on 1 July 1948, per the government guidance. If a previous owner already added a rear extension, that counts against your allowance. Many 1930s semis around Birmingham have already been extended once, sometimes without paperwork, so find out what exists before assuming you have a clean slate.
Nothing in front of the principal elevation
An extension cannot be built forward of the principal elevation, which is usually the front of the house facing the road. On corner plots or houses set at an angle to the highway, working out which wall is the principal elevation is not always obvious, and councils have disagreed with owners on exactly this point. If you are on an unusual plot, ask your council. We cover front additions in more detail in our guide to front extension permitted development in the West Midlands.
The 50% rule
All extensions and outbuildings together cannot cover more than 50% of the land around the original house. Garden sheds, garages and a previous extension all use up part of that. Count them.
Eaves near boundaries
If any part of the extension is within 2 metres of a boundary, the eaves cannot exceed 3 metres in height. This is a common reason a design that looked fine on paper needs a lower roofline.
Materials
Exterior materials must be of a similar appearance to the existing house. The Planning Portal's extensions guide notes the only exception is a conservatory. A modern glazed box in contrasting cladding is a design choice that may need an application.
Single-storey rear extensions
Rear extensions are the most searched-for PD project, and the limits depend on your house type.
| House type | Standard limit beyond original rear wall | With prior approval |
|---|---|---|
| Detached | 4 metres | 8 metres |
| Semi-detached, terraced or any other house | 3 metres | 6 metres |
The figures come from the Planning Portal's single-storey extension guide. The larger limits apply only on land that is neither designated land nor a Site of Special Scientific Interest, and they require you to apply for prior approval first.
What the 6 metre and 8 metre route involves
Prior approval is not full planning permission, but it is not a free pass. You notify the council, and it assesses specific matters, typically the effect on neighbours. You cannot start until the process is complete. If neighbours object, the council weighs their concerns, so a long extension beside a close neighbour deserves a conversation over the fence first.
Measuring properly
Measure from the original rear wall, not from a later addition. Stepped rear walls and outriggers, common on Victorian and Edwardian terraces in Birmingham, make this harder, and the answer can change what you are allowed. If the original house has an outrigger, ask your council or a designer to confirm the measurement point on a drawing before you commit to a layout.
Height
A single-storey extension must stay under 4 metres in height overall, and the eaves limit of 3 metres applies within 2 metres of a boundary. For internal head room, see our note on minimum ceiling heights, which affects floor build-ups and the usable room height.
A worked example
Take a typical 1930s semi in Solihull with a 12 metre rear garden and no previous extension. The standard limit lets you build 3 metres out. With prior approval you could go to 6 metres, enough for a kitchen-diner with room for a dining table and a sofa area. If the house has a 2.5 metre outrigger already, the measurement and the 50% ground coverage calculation need to be checked on a plan before you rely on either figure.
Side extensions
The Planning Portal's extensions guide sets out three limits for a side extension:
- It must be single-storey.
- It cannot exceed 4 metres in height.
- Its width cannot be more than half the width of the original house.
It also cannot go forward of the principal elevation, and it is not allowed on designated land. Side extensions are common on detached and semi-detached houses with a driveway or gap between properties. A single-storey side extension might hold a utility room, a downstairs shower room or a home office.
One trap: a side extension that joins a rear extension (a wrap-around) is judged against extra conditions, because the combined structure extends beyond a side elevation. Many wrap-arounds need planning permission for this reason. Our guide on side extension planning rules in the West Midlands goes through how this plays out in practice.
If you live in a semi-detached house, also read our note on semi-detached extension ideas and party wall surprises, because building up to a shared boundary is where disputes start.
Two-storey extensions
Two-storey extensions can be permitted development, but the conditions are stricter. According to the Planning Portal's two-storey extension guide:
- They are not permitted on designated land such as national parks and conservation areas.
- They must not extend beyond the original rear wall by more than 3 metres.
- They must not be within 7 metres of the boundary opposite the rear wall.
- Any two-storey extension to the side or front requires planning permission.
Upper-floor side windows must be obscure-glazed and non-opening, unless the opening part is at least 1.7 metres above the floor, per the extensions guide.
The 7 metre boundary condition rules out many modern estate plots, where gardens are short. On a typical Birmingham semi with a 10 to 12 metre garden it is usually workable, but measure it. Our overview of two-storey extension rules shows how councils tend to treat these. A related check, the 45 degree rule, is often applied by councils when they judge the impact on a neighbour's window, and it is easier to run before you draw than after.
Conservatory or extension?
A conservatory is generally assessed under the same Class A limits as an extension, so a glazed room that fits the limits does not need planning permission either. The difference tends to be building regulations: a conservatory can sometimes be exempt if it is separated from the house and meets conditions, while a proper extension opened into the house will be covered. We explain the practical differences in conservatory vs extension.
Prove it: the Lawful Development Certificate
PD means you do not need permission, but nobody gives you a document saying so. A Lawful Development Certificate (LDC) from your local planning authority confirms that your proposed works are lawful, as the government guidance explains. It is optional, but it is worth the fee for three reasons:
- Buyers' solicitors will ask for evidence when you sell.
- It protects you if a neighbour complains to the council.
- It forces the council to check your measurements before you build, not after.
You apply with scaled drawings of the existing and proposed house. This is where accurate surveys pay for themselves. For help on what a drawing pack should include, see our guide to extension planning drawings.
When to apply for planning permission instead
PD is not always the best route, even where you qualify. Consider a planning application when:
- Your design is a few centimetres over a limit. A householder application can approve a deviation that PD cannot.
- You want a wrap-around, a taller roof or a design that does not match the existing materials.
- You are in a conservation area or an Article 4 area.
- You want certainty before spending on construction drawings.
A planning approval also sits on the property's record in a way that is easy for a buyer's solicitor to read. If you are still weighing up whether to extend at all, our extend or move questions help you decide.
Our perspective
Most homeowners who contact us in Birmingham and Solihull have already read that they "can build 6 metres without planning". The figure is real, but it hides the work around it: checking for Article 4 Directions, measuring from the original wall, counting earlier extensions, and getting the prior approval application right. The mistakes we see are rarely about the headline limit. They are about assumptions made before anyone measured.
Our approach is to check eligibility and a realistic budget before any survey, then decide with you whether PD, prior approval or a full application suits the design you want. A slightly smaller extension that is quick to approve is sometimes better than a bigger one that stalls. A good design should serve how you live, not just fit a limit.
We handle planning and building regulations as part of a single managed process, so the person who checks your rights is the same team that builds the extension. That means fewer handovers and fewer surprises.
— Raja
Planning an extension in the West Midlands?
If you want a second opinion on whether your plan fits permitted development, we can help. We design and build single-storey, double-storey, kitchen, rear, side-return, wrap-around and over-garage extensions across the West Midlands, with one team looking after planning, building regulations, budget and construction. Tell us about your house through Extension Kings, or read our extension cost guide for the West Midlands to see how budgets are built up. For party wall questions on a boundary build, our guide to the party wall agreement for an extension explains what applies.
FAQ
Can I build a 3 metre extension without planning permission?
Usually yes, if your house is not a flat, is not in an area where an Article 4 Direction removes the rights, and the design meets the other limits. A semi-detached, terraced or other non-detached house can extend 3 metres beyond the original rear wall, and a detached house 4 metres. Height, eaves, materials and the 50% ground coverage limit still apply.
How big can an extension be without planning permission?
For single-storey rear extensions the limits are 3 or 4 metres, or 6 or 8 metres with prior approval, depending on house type. A side extension can be up to half the width of the original house and 4 metres high. Combined extensions and outbuildings cannot cover more than 50% of the land around the original house.
Do I need building regulations approval for a permitted development extension?
Yes, in almost all cases. Permitted development only removes the need for a planning application. Your extension still has to meet building regulations for structure, insulation, fire safety and drainage, and you may also need to serve notices under the Party Wall etc. Act.
Are the rules the same across the UK?
No. The figures in this article apply to England. Wales, Scotland and Northern Ireland have their own permitted development orders with differences in detail, so check the relevant government or council guidance if your house is outside England.
Sources
- Permitted development rights for householders: technical guidance (GOV.UK)
- Single-storey extension mini guide (Planning Portal)
- Two-storey extension mini guide (Planning Portal)
- Extensions guide (Planning Portal)